Many new vehicles are outfitted with automatic or driver-assistive steering systems, such as Lane Keeping Systems (LKS) or automatic steering functions. Such systems assist the driver in staying within a given roadway lane by, for example, exerting a low level of torque to the vehicle's steering system or applying differential braking to the wheels.
There currently exist robotic steering controllers for use in highly dynamic vehicle evaluations, where high levels of steering torque, large steering angles and high angular rates are required. These robotic steering controllers generally comprise a direct-drive or geared motor mounted to a vehicle's steering wheel, and are equipped with a load reaction mechanism to react the steering loads through rods, or other linkages attached to vehicle structure, windshield, etc. These systems generally have large self-inertia, damping, and friction characteristics, which affect the free response characteristics of the vehicle's steering system while they are installed or connected to the steering wheel. When evaluating an LKS, the contribution of the robotic steering controller's own dynamics can affect the performance of the LKS, which is undesirable.
In order to use existing robotic steering controllers for these types of evaluations, the undesirable effects of the robotic controller's own inertia, damping and friction characteristics must be accepted or electronically compensated through the use of high-fidelity torque sensors, high bandwidth controllers and inertia/damping/friction compensation algorithms. Such systems tend to be fairly expensive and complex, and often require careful tuning in order to minimize the effect of the robotic steering controller on the vehicle's own steering system dynamics. In many cases, the effect of the robotic steering controller cannot be completely eliminated through tuning, due to minute variations in the controller's own friction or damping characteristics resulting from wear, temperature changes, or other factors, and the controller consequently continues to exert residual torque on the vehicle's steering system, disturbing its free response.
Therefore a need exists to measure the free response of the steering/vehicle system without affecting its dynamics. Further, a novel approach to a robotic steering controller is needed to facilitate the evaluation of such systems in a precisely controlled manner.